(Reuters) - Attorneys for the man charged with mass murder for shooting dozens of people at a Colorado movie theater have asked the U.S. Supreme Court to force a reporter to reveal confidential sources she used for a story about the massacre.

James Holmes, 26, faces the death penalty in the shooting rampage that killed 12 people and injured dozens more at a screening of the Batman film “The Dark Knight Rises” on July 20, 2012.

His attorneys filed a petition on Thursday, asking the Supreme Court to consider overturning a 2013 ruling by New York’s top state court, the Court of Appeals, which found that New York’s journalist shield law protected Fox News reporter Jana Winter from being compelled to testify in Holmes’ case in Colorado.

Holmes’ lawyers said Winter’s testimony is necessary to determine the identity of law enforcement officials who violated a gag order and divulged some of the contents of a notebook Holmes allegedly sent to a psychiatrist before the shooting incident.

According to the petition, the Court of Appeals decision “eviscerated” a law adopted in all 50 states that allows prosecutors or criminal defendants to subpoena witnesses located in other states. Excluding New York-based journalists from the law, Holmes’ attorneys said, would trigger a “slippery slope of exceptions” that could deny defendants their fair trial rights.

“Without action by this Court, no state can be assured that any other state will abide by the uniform act,” the petition reads.

A Fox News spokeswoman did not immediately return a request for comment.

Holmes is set to go on trial in October on multiple counts of first-degree murder and attempted murder. He has pleaded not guilty by reason of insanity.

As part of their investigation, police took possession of a notebook Holmes had mailed to a psychiatrist shortly before the shootings. The judge handling the case subsequently issued a gag order barring police and attorneys from divulging the contents of the notebook to the public.

The day the order was issued, Fox News published an online story by Winter claiming the notebook was “full of details about how (Holmes) was going to kill people.” It indicated two unnamed law enforcement officials had shared the information with her.

Holmes’ attorneys moved to sanction the officials responsible for the leak. The 14 officials who had knowledge of the notebook’s contents all denied speaking with Winter, according to the Court of Appeals.

As a result, Holmes’ team sought to compel Winter to testify about her sources.

Holmes’ attorneys maintained that any issues related to the exposure of confidential sources should be decided under Colorado’s shield law, which allows judges to order reporters to disclose sources, if it is deemed “material and necessary.”

Winter’s lawyers argued New York’s more expansive law applied and being ordered to testify would result in the end of her career as a journalist or, if she refused, her incarceration.

The Court of Appeals in December agreed with Winter, saying that because New York is the media capital of the country, journalists based there must be afforded extraordinary protections.